title: Vector analysis of evolutive corneal astigmatic changes in keratoconus.
abstract: OBJECTIVE
  To evaluate by vector analysis the corneal astigmatic changes occurring in keratoconic corneas during a 3-year follow-up and to determine the relationship between these changes and other clinical changes.
  
  
  METHODS
  Keratoconic eyes (n = 114) of 75 patients ranging in age from 14 to 70 years were retrospectively reviewed in four different centers. In all cases, a 3-year follow-up was completed after the diagnosis of keratoconus. Visual, refractive, keratometric, aberrometric, internal astigmatism (IA), and pachymetric changes were evaluated during the follow-up. In addition, corneal astigmatic changes were evaluated by examining the following parameters, using a modification of the Alpins vectorial method: evolutive astigmatism (EA) and angle of error (AE).
  
  
  RESULTS
  An increase in the magnitude of refractive (P = 0.02) and corneal astigmatism (P = 0.05) was found. The mean magnitude of EA was 1.21 ± 0.97 D at 3 years, with no significant changes at each annual visit (P ≥ 0.52). Mean absolute AE increased significantly by the end of the follow-up (P < 0.01). Absolute AE and the increase in corneal astigmatism were found to correlate at 2 years (r = 0.675, P < 0.01). This correlation became poorer at 3 years (r = 0.352, P = 0.02). The magnitude of the EA was also found to be significantly correlated with central corneal thinning (r = -0.441, P = 0.02). Multiple regression analysis revealed that the magnitude of EA at 3 years correlated significantly with the baseline sphere and IA (R² = 0.86, P < 0.01).
  
  
  CONCLUSIONS
  Corneal vector astigmatic changes are related to some signs of keratoconus progression and are therefore predictive.
authors.affiliation: Keratoconus Unit, Vissum/Instituto Oftalmológico de Alicante, Alicante, Spain. dpinero@vissum.com
authors.forename: David P
authors.initials: DP
authors.lastname: Piñero
authors.forename: Jorge L
authors.initials: JL
authors.lastname: Alio
authors.forename: Javier
authors.initials: J
authors.lastname: Tomás
authors.forename: Miguel J
authors.initials: MJ
authors.lastname: Maldonado
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Teus
authors.forename: Rafael I
authors.initials: RI
authors.lastname: Barraquer
mesh_terms: D057128:Aberrometry; D000293:Adolescent; D000328:Adult; D000368:Aged; D001251:Astigmatism / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D003316:Corneal Diseases / Q000175:diagnosis / Q000209:etiology* / Q000503:physiopathology; D019781:Corneal Topography; D003941:Diagnostic Techniques, Ophthalmological; D018450:Disease Progression; D005500:Follow-Up Studies; D006801:Humans; D007640:Keratoconus / Q000150:complications* / Q000503:physiopathology; D008297:Male; D008875:Middle Aged; D012372:ROC Curve; D012029:Refraction, Ocular; D012030:Refractive Errors / Q000175:diagnosis / Q000209:etiology / Q000503:physiopathology; D012044:Regression Analysis; D012189:Retrospective Studies; D014065:Tonometry, Ocular; D055815:Young Adult